1. Field of the Invention
The present invention relates to a recording apparatus wherein toner images formed on the toner image-carrier are transferred onto the recording material.
2. Description of the Prior Art
The outline of the conventional recording apparatus wherein a toner image-carrier is used will be explained below with an example of an electrophotographic copying machine that is of a scanning exposure type. A document to be copied is put on the platen and a copy button is depressed, then the exposure lamp travels in the fixed direction together with an optical system having a reflection mirror and others, irradiating the document. The reflected light corresponding to light and shade of the document is irradiated onto the toner image-carrier (e.g., photoreceptor) that is electrically charged uniformly through aforesaid optical system and thereby electrostatic latent images are formed on the toner image-carrier. Further, toner images corresponding to the density of the document are formed on the photoconductor drum with the aid of developer.
On the other hand, a recording material (e.g., a copy paper) is fed from the paper-feeding device so that it coincides with the position of toner images on the toner image-carrier and then it contacts the toner image-carrier. And then the toner images formed on the surface of the toner-image carrier are transferred to the copy paper with the aid of the transferring electrode, as the toner image-carrier continues rotating in the fixed direction. After that, the copy paper on which the toner images are transferred separates from the toner image-carrier, and it is fed to the roller fixing unit. The roller fixing unit is comprising two rollers at least one of them is heated and it heats and fixes the images formed with the aid of developer on the copy paper. After this, the copy paper is sent out from the copying machine. Meanwhile, the toner image-carrier, after the visible images of toner thereon are transferred to the copy paper, is refreshed by removing remaining toner. And this recording process repeats for every recording. However, when the toner images formed on the toner image-carrier are transferred electrostatically on the copy paper through the transferring electrode such as a corona discharger for example, there is accompanied a disturbance in the electric charge which decreases the resolution of toner images. When the conductive and magnetic toner is given, as a developer in the electrostatic transfer system, the transferring of toner image is substantially impossible.
As a method to improve aforesaid disadvantages in the electrostatic transferring, there has been tried a method wherein pressure rollers press and transfer the images on the transfer sheet but this method has troubles that the transferring efficiency is poor and only half of the toner of toner images is transferred.
In Japanese Patent Examined Publication Nos. 41679/1971 and 22763/1973, Japanese Patent Publication Open to Public Inspection No. 78559/1974 and U.S. Pat. No. 3,993,825, there are proposed methods wherein aforesaid toner images on the toner image-carrier are pressed and transferred on an intermediate transfer member whose transferring layer is made of rubber, and then the images thus transferred on the intermediate transfer member is transferred and fixed concurrently (transfer fixing) on the copy paper by heating and melting of toner caused by a heat roller. In such a method, toner images are pressed and transferred on the outermost layer of the transferring layer made of a rubber, such as silicone rubber or fluorine rubber having a mold releasing property on the one hand and having, on the other hand, the property that adheres fine particles by pressure. Accordingly, the toner images adhered on the transferring layer of the intermediate transfer member are heated, then melted, and then these melting toner images are pressed, and transferred on the copy paper by the releasing property and are finally fixed. Namely, the toner images melted through heating are easily transferred on the copy paper owing to aforesaid mold releasing property of the transferring layer and are fixed. Therefore the resolution of the toner images does not fall through the transferring step, and the transferring rate is high.
The copy paper used for the copying machine wherein the intermediate transfer member is employed should have been heated fully before contacting the intermediate transfer member in order for the toner images on the intermediate transfer member to be transferred and fixed suitably. Consequently, copy paper is required to be fed so that the copy paper contacts the intermediate transfer member after being heated previously by a heat roll or heat plate.
Now, the copy paper generally contains moisture of 4-7% by weight, and when heated, such moisture evaporates and water vapor is produced. Water vapor, when cooled, becomes waterdrops which adhere to the neighboring substances and make them wet.
In the case of a roll type intermediate transfer member, for example, in order to make recording apparatus compact, the heat roll for heating preliminarily the copy paper and other members for the recording process is arranged near the toner image-carrier. However, the water vapor produced from the copy paper might come in touch with the toner image-carrier. If the surface of the toner image-carrier (for example, photoreceptor) touches the water vapor, the water vapor condenses into waterdrops adhering to the photoreceptor because the photoreceptor is kept at a relatively low temperature.
When the toner image-carrier gets wet by waterdrops thereby, the remaining toner on the toner image-carrier condenses and adheres firmly to the toner image-carrier. The toner powder adhered to the wet area on the toner image carrier or the toner powder which is wetted by waterdrops is hard to be removed perfectly by the cleaning unit. Consequently the toner image-carrier, in this case, undergoes the repetition of cycles of charging and others for the next copying, being covered by remaining toner powder. When the toner image-carrier is covered by unexpected toner powder, the area where the toner powder adheres will not be exposed and will not leak charges. Therefore in the developing step, the toner powder further adheres to the area where toner powder previously have adhered, and this is transferred to the copy paper in the transferring step.
Namely, when the toner image-carrier is wetted, the stains or stripes caused by the condensed toner powder adhered to the toner image-carrier 1 appear on the copy paper, which results in the copy being illegible. Likewise, due to waterdrops adhered on the toner image-carrier, normal charging is interrupted and troubles happen in the process of exposure and development.
Further, the toner image-carriers are mostly made of a photoreceptor and the characteristic of the photoreceptor is easily changed by the heat. Therefore, if a heating member is arranged near the toner image-carrier, the heat from the heating member effects the property of charging, then the latent image density will be changed, and troubles take place in recording process.